Sou iniciante em sliverlight e MVVM. Não consigo vincular a propriedade de bloco de texto de outra classe à classe de interface do usuário usando o MVVM.

Meu código está aqui. Informe-me como vincular a propriedade de bloco de texto abaixo em Authentication.cs.

MainPage.xaml

<TextBlock Height="30" Margin="122,218,0,0" Name="textBlock3" Text="{Binding Path=ErrorStatus, Mode=TwoWay}" VerticalAlignment="Top" HorizontalAlignment="Left" Width="86" />

MainPage.xaml.cs

private Authentication authentication;

// Constructor
public MainPage()
{
    InitializeComponent();
    this.DataContext = authentication;
}

ViewModelBase.cs

public class ViewModelBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void NotifyPropertyChanged(String info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }
}

Authentication.cs

public class Authentication : ViewModelBase
{
    private string _ErrorStatus;
    public string ErrorStatus
    {
        get
        {
            return _ErrorStatus;
        }
        set
        {
            _ErrorStatus = value;
            NotifyPropertyChanged("ErrorStatus");
        }
    }

    void Authenticate()
    {
        //Here, I write authentication code....
        //After the authentication code, I want to change textBlock property depend on auth status.
        //Please let me know how to write code.
    }
}